Spark plug



April 7, 1931.

H. GERDIEN EIT AL SPARK PLUG Filed Dec. w8, 1928 s 4 o j MM mumm-Patented Apr. '7, 1931 `uNrrEn STATES HANS GERDIEN, F BERLIN-GRUNEWALD,AND REINHOLD REICHMANN, OF BERLIN,

GERMANY, ASSIGNORS T SIEMENS & HALSKE' AKTIENGESELLSCHAFT, 0F

SIEMENSSTADT, NEAR BERLIN, A CORPORATION 0F vGERMANY SPARK PLUG-appuemon med'necember s, 192s, sei-iai No.

Our invention relates to improvements in spark plugs.

It is already known to construct the insulators of spark plugs ofquartz, if preferred in two parts. It has, for instance,- been proposedto construct the lower part only of the insulator, adjacent to the sparkgapand subjected to the highest tempera-y tures, of quartz.

According to ourNinvention at least that part of a two-part insulator ofa spark plug which is adjacent to the spark gap, or the end facing thecombustion chamber of the engine is constructed of aluminum-oxide. Theinsu ator may be constructed of aluminumoxide, produced from sintered orfused alu- 4 minum-oxide, such as artificial sapphire or structed ofaluminum-oxide.

ruby. Sintered and fused aluminum-oxide is indiier'ent to temperaturefluctuations,

like quartz glass. It is, further, atthe high temperatures in questionless subject to reactions, so that its surface facing the combustionchamber is not attacked in an way. It may be advisable to olish this surace, so that any particles of car n preci itated upon it are easilydislod d and thus t e plug oes not become chokecby carbon deposits.

In the drawings attached hereto and forming part of our specificationtwo embodiments of our invention are illustrated by way of example.

In the drawings- Fig. 1, represents a longitudinal section throughA oneconstruction of our improved spark plug, and

Fi 2, a longitudinal section through a m cation of the plug. v

Referring to Fig, 1 ofthe drawings, 1 is the lpart of the insulatordirectly exposed to the ot products of combustion in the engine, whichpart according to our invention is con- 2 is the main portion of theinsulator, mound in' the i socket 4.by means of the-packings '3 in thecustomary manner. The central electrode-5 main rtion2 of-thensulator andthe tipl 1` are joined between this collar 6 and a clampdevice, such asa nut, located atthe outer elili of the ignition electrode.

324,604, and in Germany December 23, 1927.

Fig. 2 illustrates at 7--a different design of the insulator portion,which according to our invention is constructed of aluminum-oxide.

The remaining parts of .the spark pl are assumed to be similar to thoseshown in ig. 1 and are indicated by the like numeralsv of reference. Theend of the insulator portion 7 is .outwardly and inwardly tapered and isprovided at. its thicker end with a flange, which abuts against the mainportion 2 of the insulator. The surface of the tapering part 7 ispreferably highly finished, so that no carbon or .the like can adhere toit.

On account of the' high costs caused by machining fused a1uminum-oxide,the insulator tip is preferably produced by sintering aluminum-oxide attemperatures of more than 1600 C.

The manufacture of sintered insulators for spark plugs is preferablycarried out in. the following manner: A

The aluminum-oxide is, prior to the sintering process, moulded by one ofthe meth- "ods known in the art, dried and then sinhardly diiiers fromthose vmade of fused aluminum-oxide yregardin its refractory andinsulatin quallties. ts production is', however, far ess expensive,because the high costs of machining are eliminated.

The manufacture of the insulator may be 'started from ordinaryaluminum-oxide as well as from an loxide which has been subjected to apreliminary fusing. As it is comaratively easy to produce large-sizeinsua'tors b sintering, not onl the portion of the insu ator subject tothe ighest temperatures should be made ofaluminum-oxidesiny -tered atover 16,00 C., but the entire insulator. is provided with a collar orshoulder 6. The

, Careful tests have liroventhat aluminum oxide for' insulators producedas described hereinbefore is superiorto all other materials 105electrodes, an

chemical attacks by combustion products in the cylinder, in particularalso its resistivity to so-called anti-knocking metal'compounds nowfrequentl added to the fuel, because s aluminum oxi e does not formcompounds with these combustion products. It should be n oted that forinstance the glazing of porcelain insulators which consists of 'sili`well known to crack at quick variations in temperature.

5. On account of its hightelectric insu-- lating quality not impaired bychemical reactions with the combustion products. Also this r uirement isnot fulilled b porcelain.

mounting said electrodes, said insulator consisting at the end facingthe combustion chamber substantiallyentirely of aluminum-oxide.

3. A spark plug, comprising conducting electrodes and an insulatorconsisting'of sintered aluminum-oxide.

4. A spark plug, comprisinglconductin electrodes andan insulator formounting sai electrodes, said insulator consisting at least l at the endfacing the combustion chamber of the engine of sintei'ed aluminum-oxide.5. A spark plug, comprising conducting electrodes and lan insulatorconsisting substantially entirely ofl aluminum oxide, sintered atsuitable temperatures vto form a sub-A stantially crystalline body.

6. A spark plug, comprising conducting electrodes and an insulator formounting said electrodes, said. insulator consisting at lthe end facingthe combustion chamber substantiallyentirely of aluminum oxide sinteredat suitable temperatures to form a sub'- stantially crystalline body.

In testimony whereofwe aix our signatures.

HANS GERDIEN. REINHOLD REICHMANN.

-6. uminum oxide has great ensity ren- 30 dering it impermeable togases, and

7.' t iseasily molded into any desirable v form vin unsintered conditionand, there? fore, -easily manufactured by sintering at -hightemperatures.. With respect to points 'so 6 and 7 porcelain wouldfulfill these requirementslinasmuch as porcelain has great density, and:when glazed is impermeablev to n gases and can be molded before it isred.

In some of the annexed claims we have 4 characterized the insulator asconsisting substantially entirely of aluminum oxide, by which we meanthat the insulator thus produced consists of substantially pure aluminumoxide, excepting such impurities 4,5 as would not have any eiect uponthe aforementioned properties.-l l

The use of our insulator of fused or sini tered aluminum-oxide isparticularly advantageous, if the internal combustion engine v 50 is fedwith fuel containing metalcom ounds,

and in which the precipitation of con ucting layers upon'the msulator iseasily possible. The insulator'consist' of aluminum-oxide may beprovided in we the creeping path. Various modifications and chan es maybe made without 'departing from t e spirit .and the of the mventlon.VeAclalm ol'r invention: spar p -comprsin .con uctin electrodes and.aiiginsulator cosisting sub stantially'entirel ofaluminum-oxide. 2. Aspark ,y com risingconducting an ator serving for lll known manner with'l5 petticoatsin .order to increase the length of

